In recent years, for example, in liquid crystal displays and organic EL displays, a method for enhancing the aperture ratio of a display device is known as a method for achieving further higher precision and higher resolution (refer to Patent Document 1). This is a method in which a transparent heat-resistant planarization film is prepared on a TFT device to transmit light with more efficiency by applying a planarization material onto the TFT device formed on a substrate and thermally curing the material.
The materials used as the planarization films for TFT substrates are required to become highly heat resistant and highly transparent after curing, and as the materials having these characteristics, polysiloxane and silicone polyimide precursor are known (refer to Patent Documents 2, 3, 4).
Generally, when an organic compound is used for the planarization films for TFT substrates, its cured film had a problem that an adequate adhesiveness to a substrate surface or a device surface composed of metal or an inorganic substance is not achieved in addition to the problems of heat resistance and transparency. Therefore, a composition made by adding a silane coupling agent to a phenolic resin and a quinone diazide compound for improving the adhesiveness (refer to Patent Document 5), and a composition made by adding a silane coupling agent to an acrylic resin and a quinone diazide compound (refer to Patent Document 6) are known. In either technology, the silane coupling agent is added in order to improve adhesiveness to a substrate. However, when the silane coupling agent is added to polysiloxane for the same purpose, an adequate adhesiveness to a substrate surface or a device surface can be achieved without impairing high heat resistance and high transparency, but there is a problem that strains or cracks are generated depending on kinds of solvents used in a resist-stripping treatment by an alkaline solvent, which is performed to process an upper layer of a cured film after forming the cured film.
Further, it is known that the adhesiveness is improved by adding aromatic bisimide oligomer to polyimide (refer to Patent Document 7). However, since aromatic bisimide oligomer has absorption in a visible light region, the addition of the aromatic bisimide oligomer to polysiloxane enables to provide adequate adhesiveness to the substrate surface or the device surface and inhibit the occurrence of cracks due to an alkaline solvent, but it causes a problem of transparency.
On the other hand, a silicone polyimide precursor has an excellent adhesiveness to the substrate surface or the device surface and crack resistance against the alkaline solvent because it has a structure of a silane coupling agent at the end and a cured film formed from the silicone polyimide precursor has an imido bond, but the silicone polyimide precursor has large shrinkage during curing in its conversion to imido by heat because it has an amic acid structure and therefore it does not have sufficient planarization characteristics.    Patent Document 1: Japanese Patent Publication No. 2006-227649 (claim 1)    Patent Document 2: Japanese Patent Publication No. 2006-18249 (claim 1)    Patent Document 3: Japanese Patent Publication No. 8-259894 (claims 1, 2)    Patent Document 4: Japanese Patent Publication No. 9-291150 (claim 1)    Patent Document 5: Japanese Patent Publication No. 2003-43688 (p. 8)    Patent Document 6: Japanese Patent Publication No. 2005-49691 (p. 18)    Patent Document 7: Japanese Patent Publication No. 10-1542 (claim 1)